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3. Use the bond energies in the table to answer the following questions:

\begin{tabular}{|l|c|}
\hline Bond & Bond energy [tex]$/ \text{kJ/mol}$[/tex] \\
\hline [tex]$H - H$[/tex] & 436 \\
\hline [tex]$O - H$[/tex] & 464 \\
\hline [tex]$O = O$[/tex] & 497 \\
\hline
\end{tabular}

Given the following reaction:
[tex]\[ 2 H_2 + O_2 \rightarrow 2 H_2O \][/tex]

a) Which bonds are broken?

b) What is the total bond energy of the bonds that are broken?

c) Which bonds are formed?

d) Calculate the total energy given out when the bonds are formed.

e) Calculate [tex]$\Delta H$[/tex] for the reaction and state whether it is endothermic or exothermic.

Sagot :

GinnyAnsweridn
Let's analyze the given reaction step by step:

### Given Reaction
[tex]\[ 2 H_2 + O_2 \rightarrow 2 H_2O \][/tex]

### Bond Energies from the Table
- [tex]\( H - H \)[/tex]: 436 kJ/mol
- [tex]\( O - H \)[/tex]: 464 kJ/mol
- [tex]\( O = O \)[/tex]: 497 kJ/mol

### a) Which bonds are broken?

In the reaction, the bonds that need to be broken are:
- The bonds in two [tex]\( H_2 \)[/tex] molecules.
- The bonds in one [tex]\( O_2 \)[/tex] molecule.

### b) What is the total bond energy of the bonds that are broken?

To find the total bond energy of the bonds broken:
- Each [tex]\( H_2 \)[/tex] molecule has one [tex]\( H-H \)[/tex] bond.
- Energy for one [tex]\( H-H \)[/tex] bond: 436 kJ/mol
- For 2 [tex]\( H_2 \)[/tex] molecules: [tex]\( 2 \times 436 \)[/tex] kJ/mol = 872 kJ/mol
- [tex]\( O_2 \)[/tex] molecule has one [tex]\( O=O \)[/tex] bond.
- Energy for one [tex]\( O=O \)[/tex] bond: 497 kJ/mol

Total bond energy for bonds broken:
[tex]\[ 872 + 497 = 1369 \text{ kJ/mol} \][/tex]

### c) Which bonds are formed?

In the reaction, the bonds that are formed are the [tex]\( O-H \)[/tex] bonds in the water molecules:
- Each [tex]\( H_2O \)[/tex] molecule has two [tex]\( O-H \)[/tex] bonds.
- Since 2 [tex]\( H_2O \)[/tex] molecules are formed, there will be [tex]\( 2 \times 2 = 4 \)[/tex] [tex]\( O-H \)[/tex] bonds formed.

### d) Calculate the total energy given out when the bonds are formed?

To find the total bond energy of the bonds formed:
- Each [tex]\( O-H \)[/tex] bond has energy: 464 kJ/mol
- For 4 [tex]\( O-H \)[/tex] bonds: [tex]\( 4 \times 464 \)[/tex] kJ/mol = 1856 kJ/mol

### e) Calculate [tex]\(\Delta H\)[/tex] for the reaction and state whether it is endothermic or exothermic.

The enthalpy change [tex]\(\Delta H\)[/tex] for the reaction is calculated as:
[tex]\[ \Delta H = \text{Total bond energy of bonds broken} - \text{Total bond energy of bonds formed} \][/tex]

Given:
- Total bond energy of bonds broken: 1369 kJ/mol
- Total bond energy of bonds formed: 1856 kJ/mol

Thus:
[tex]\[ \Delta H = 1369 - 1856 = -487 \text{ kJ/mol} \][/tex]

Since [tex]\(\Delta H\)[/tex] is negative, the reaction releases energy, making it exothermic.

### Conclusion

- Total bond energy of bonds broken: 1369 kJ/mol
- Total bond energy of bonds formed: 1856 kJ/mol
- [tex]\(\Delta H\)[/tex] for the reaction: -487 kJ/mol

Therefore, the reaction is exothermic.
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